3.2.5. Effect of extract dilution before SPE procedure on extraction efficient
The analysis of drug residues in fatty matrices is yet a challenging issue, because of the inherent complexity of the matrix. In fact, it is very difficult to avoid the co-extraction of fatty material. Since, high recoveries of drugs have to obtained in a ideally fat-free extract, an additional clean-up step is usually included prior to subsequent steps in the analytical process. In this study SPE was used as a clean-up step.
The extract obtained after UAE is usually evaporated, then the residue is dissolved in water and SPE procedure is applied. In this case after CT-99021 the extracts, the drugs remain in the undissolved fat and the recoveries were very low. The evaporation step could not be applied. On the other hand, organic solvents disrupt interaction between the compound and SPE sorbent functional groups. For this reason the methanol extract cannot be pass directly through the SPE sorbent.
Therefore, the extract from UAE was diluted with water to 150, 250 or 350 mL. This dilution step was necessary in order to lower the percentage of organic solvent being dissolved in the aqueous phase which otherwise would lower the extraction efficiencies due to an undesirably high elution strength in the SPE procedure. After reduction the percentage of methanol by diluting in 350 mL of water, SPE can be applied without decreasing of recoveries for all selected compounds (Fig. 6).